U.S. patent number 4,891,653 [Application Number 07/185,904] was granted by the patent office on 1990-01-02 for image recorder with microstep driven motor transport.
This patent grant is currently assigned to Minolta Camera Kabushiki Kaisha. Invention is credited to Akiyoshi Hamada, Mitsutoshi Yagoto.
United States Patent |
4,891,653 |
Hamada , et al. |
January 2, 1990 |
Image recorder with microstep driven motor transport
Abstract
An image forming apparatus for forming in series a plurality of
images on a photosensitive film of the long roll type having a film
transporting mechanism using a stepping motor, a microstep driver
for controllably driving the stepping motor in a plurality of
microsteps constituting one step unit of the stepping motor and an
imaging device for forming an image on the film being transported
by the film transporting mechanism. According to this image forming
apparatus, variations in the film transport start positions
resulting from the microstep-wise drive are avoided either by the
film transporting mechanism arranged such that a pitch between
adjacent images to be formed in series on the film is a multiple of
an integer of a film transport distance covered by the single step
unit of the stepping motor, or by an initial control device for
re-setting the stepping motor to a stop position thereof assumed at
completion of a previous imaging operation before re-energizing the
stepping motor for a next imaging operation.
Inventors: |
Hamada; Akiyoshi (Osaka,
JP), Yagoto; Mitsutoshi (Osaka, JP) |
Assignee: |
Minolta Camera Kabushiki Kaisha
(Osaka, JP)
|
Family
ID: |
26444375 |
Appl.
No.: |
07/185,904 |
Filed: |
April 25, 1988 |
Foreign Application Priority Data
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Apr 27, 1987 [JP] |
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62-103781 |
Apr 27, 1987 [JP] |
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62-103782 |
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Current U.S.
Class: |
347/262;
358/296 |
Current CPC
Class: |
G01D
15/14 (20130101); G03D 13/002 (20130101) |
Current International
Class: |
G01D
15/14 (20060101); G03D 13/00 (20060101); G01D
015/24 (); G01D 015/14 (); H04N 001/23 () |
Field of
Search: |
;346/17R,108,160,76L
;358/296,300,302 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
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57-193170 |
|
Nov 1982 |
|
JP |
|
59-116748 |
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Jul 1984 |
|
JP |
|
Primary Examiner: Reynolds; B. A.
Assistant Examiner: Reinhart; Mark
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
What is claimed is:
1. An image forming apparatus for forming in series a plurality of
images on a photosensitive film of the long roll type
comprising:
feeding means for feeding the film;
discharging means for discharging an image-recorded film;
transporting means interposed between said feeding means and said
discharging means for transporting the film from said feeding means
to said discharging means;
a stepping motor for driving said transporting means;
a microstep driver for controllably driving said stepping motor in
a plurality of microsteps constituting one step unit of said
stepping motor;
imaging means for scanning and exposing the film being transported
by said transporting means in a direction normal to a film
transporting direction;
wherein a pitch between adjacent images to be formed in series on
the film is a multiple of an integer of a film transport distance
covered by the single step unit of said stepping motor;
said transporting means includes a platen roller driven and rotated
by said stepping motor, said platen roller having a diameter
predetermined to be of a multiple of an integer value of said film
transport distance covered by one step unit of said stepping motor;
and
wherein said platen roller is mounted on a drive shaft of said
stepping motor, said diameter: R of the platen roller, said pitch:
P of the adjacent images to be formed in series on the film being
represented by the following expression:
where N is an integer value and A is a step angle of said stepping
motor.
2. An image forming apparatus for forming in series a plurality of
images on a photosensitive film of the long roll type
comprising:
feeding means for feeding the film;
discharging means for discharging an image-recorded film;
transporting means interposed between said feeding means and said
discharging means for transporting the film from said feeding means
to said discharging means;
a stepping motor for driving said transporting means;
a microstep driver for controllably driving said stepping motor in
a plurality of microsteps constituting one step unit of said
stepping motor;
imaging means for scanning and exposing the film being transported
by said transporting mean in a direction normal to a film
transporting direction whereby when an imaging operation is
completed, a stop position for said stepping motor is determined;
and
initial control means for re-setting said stepping motor to said
stop position determined at the completion of the immediately
preceding imaging operation before re-energizing said stepping
motor for a next imaging operation.
3. An image forming apparatus, as defined in claim 2, further
comprising:
memory means for storing a number of microsteps corresponding to a
film transport distance provided by said platen roller;
wherein said initial control means executes an initial control
operation on said stepping motor in accordance with said number of
microsteps stored in said memory means.
4. An image forming apparatus, as defined in claim 2, wherein said
microstep driver supplies a current to said stepping motor for the
microstep drive of the stepping motor such that changes in the
supplied current are phased in over a predetermined period of time.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus for
recording image information by means of laser beam irradiation on a
film of the long roll type being transported by drive of a stepping
motor.
(2) Description of Related Art
There is known an image forming apparatus of the above-noted type
comprising a housing, a film delivery section for a film of the
roll type placed inside the housing, a film accommodating section
disposed in the housing for forming a film transport passage
together with the film delivery section, a main drive unit disposed
on the film transport passage in the housing and for driving the
film at a fixed speed and an image information recording section
constituted by a laser optical unit for applying a laser beam onto
the film in a width direction of the film being driven and
transported by the main drive unit. The main drive unit includes a
stepping motor and a platen roller driven by the motor for
transporting the film contacting an outer circumferential face of
the roller.
In the image forming apparatus constructed as above,
two-dimensional images are formed in series on the long-length film
by a laser beam scanning operation in the film is width direction
while the film being transported.
In order for the above apparatus to obtain an image of good
quality, it is essential that the film transport operation be
carried out at a constant and equal speed. According to one known
arrangement attempting to meet this requirement, which is shown in
FIG. 10, there is provided a microstep driver for sub-dividing one
step unit of the stepping motor powered ON and OFF by a CPU into
smaller (micro) step units, thereby minimizing such transport
irregularities or errors.
The stepping motor employed in the above-described conventional
image forming apparatus has an inherent disadvantage to be
described next. That is, the stepping motor is in a magnetically
balanced, i.e., stable state when one of its rotor pairs is opposed
to a stator. Thus, if a predetermined amount of film transport is
completed in the middle of one-step rotation of the stepping motor,
there occurs a magnetic instability such that either pair of the
rotors will stop only after automatically proceeding or receding in
its rotation to become opposed to the stator in order to regain the
stability. Therefore, if the stepping motor is re-energized for the
next film transport, this film transport operation is inadvertently
carried out from the above-noted stabilized position of the motor
which has shifted from the previous position assumed by the motor
before being re-energized. However, if an image is formed on a
long-length film as used e.g. in a page printer, its frame pitch
must be maintained exactly constant. In such case, the stepping
motor is disadvantageous because of its above-noted instability
which necessarily results in inconsistency in the frame pitch. This
problem appears conspicuously in the case of a microfilm where an
image is recorded in micron unit precision to be enlarged for use
thereafter.
Next, the frame pitch will be defined. As shown in FIG. 9, images
are formed in series in respective adjacent frames F on the film.
The frame pitch P is defined here as a pitch between an adjacent
pair of frames, i.e.,a distance: P from a leading edge of one frame
to a leading edge of the adjacent frame next in order in the
direction in which the film is transported.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide an image
forming apparatus using a stepping motor driven microstep-wise as
film transport means, the apparatus being capable of forming images
on a film with an accurately constant frame pitch.
The foregoing object is accomplished in one embodiment by providing
film transport means driven by the stepping motor, the transport
means being constructed such that the frame pitch of the images to
be formed on the film is a multiple of an integer of a film
transport distance covered by one step amount of the drive provided
by the stepping motor.
According to the above construction, when the stepping motor is
stopped after completion of a predetermined amount of film
transport, one of the rotor pairs is always placed in the
magnetically stable state as being opposed to and attracted by the
stator. Thus, there is no possibility that the predetermined amount
of film transport operation is stopped in the middle of one step
rotational unit of the motor. As the result, the leading edge of
the image to be formed next is always placed at the predetermined
leading edge of the frame pitch.
The foregoing object is also accomplished in another embodiment by
initial control means for the stepping motor. This initial control
means operates to set the stepping motor to the stop position
previously assumed by the motor at completion of the foregoing
imaging operation before the stepping motor is re-energized for a
subsequent imaging operation.
According to this arrangement, when one imaging, i.e., one frame
imaging operation is completed in the middle of one step rotation
of the stepping motor, as described hereinbefore, the stepping
motor is stopped only after proceeding or receding in its rotation
to a position where either pair of rotors is opposed to the stator.
However, with the above-noted arrangement, the stepping motor is to
be re-energized after the initial control means returns the motor
to the previous microstep drive stop position. As a result, when
starting the next imaging operation after completion of one imaging
operation, the leading edge of the next image is always placed at
the predetermined leading edge of the frame pitch.
In this case, needless to say, a diameter of a platen roller may be
predetermined freely.
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view showing an entire construction of an image
forming apparatus related to the present invention,
FIG. 2 is a control block diagram illustrating a control scheme for
a stepping motor according to one preferred embodiment of the
present invention,
FIG. 3 is a waveform chart illustrating an output waveform
generated by a microstep driver,
FIG. 4 is a control block diagram illustrating a modified control
scheme for the stepping motor alternative to that illustrated in
FIG. 2,
FIG. 5 is a control block diagram illustrating a control scheme for
the stepping motor according to a second embodiment of the present
invention,
FIG. 6 is a flow chart illustrating the control scheme in FIG. 5 to
be executed when the stepping motor is energized,
FIG. 7 is a control block diagram illustrating a first modified
control scheme alternative to that shown in FIG. 5,
FIG. 8 is a control block diagram illustrating a second modified
control scheme alternative to that shown in FIG. 5,
FIG. 9 is a schematic conceptual view illustrating a concept of a
frame pitch on a film, and
FIG. 10 is a block diagram illustrating a prior art control scheme
for the stepping motor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of an image forming apparatus related to the
present invention will be particularly described hereinafter with
reference to the accompanying drawings.
(Embodiment (1))
An image forming apparatus according to this embodiment, as shown
in FIG. 1, comprises as main components thereof a housing 100, a
film delivery section 10, a film accommodating section 20, a film
transport unit 30, an image information recording section 40 and a
heat-developing section 50.
The housing 100 accommodating therein the film delivery section 10,
a film accommodating section 20, the transport unit 30, the image
information recording section 40, the heat-developing section 50
and the like, provides a dark room interior condition shut out from
the external environment. Also, the housing 100 includes an
openable lid for inserting a film therethrough.
The film delivery section 10 is positioned at a lower portion
inside the housing and loading therein a film cassette 12 housing
the film 11 of the heat-development type in a rolled-up condition
thereof. As this film 11, a dry silver halide film (DAKOMATIC film
(trademark) manufactured by Kodak. Co.) having a length of 170 m
and a width of 16 mm is used.
The film accommodating section 20 is positioned at an upper
interior portion of the housing 100 and forms a film transport
passage 26 with the film delivery section 10, the film
accommodating section 20 including a film take-up reel 21
positioned at an upper interior portion of the housing and a tray
22 disposed outwardly of the housing for receiving a cut-off film
portion. The housing 100 further includes an unillustrated
switching device for selectively advancing the film either toward
the take-up reel 21 or towards the tray 22. For obtaining a cut-off
film, there is also provided a cutter 23 for cutting off the film
11 being transported, and then the cut-off film is received in the
tray 22.
The transport unit 30 is disposed on the film transport passage 26
at a middle interior portion of the housing 100. This transport
unit 30 includes a stepping motor, a platen roller 31 driven by the
stepping motor and pressing rollers 32 and 33 contacting the platen
roller 31 to be driven and rotated by the same, the film 11 being
transported as nipped between the platen roller 31 and the pressing
rollers 32 and 33.
The stepping motor M is of the hybrid four-phase-excitation type
having a step angle of 0.9 degree. In operation, as illustrated in
a control block diagram of FIG. 2, this stepping motor M is
controlled by a microstep driver MSD energized by an ON/OFF signal
from a microcomputer CPU. The microstep driver MSD operates to
drive and control the stepping motor M microstep-wise by
sub-dividing one step of the stepping motor M into 1024 microsteps.
FIG. 3 shows waveforms of output from this microstep driver MSD. By
receiving an electric current having the above waveforms into
respective channels, the stepping motor M is driven microstep-wise.
Such microstep drive operation of the stepping motor is wellknown
from the prior art and therefore will not be discussed here in
detail. A step counter denoted by a reference mark SC in FIG. 2
counts step-like pulses generated from the microstep driver MSD to
the stepping motor M and then transmits a completion signal to the
microcomputer CPU after counting up a predetermined number of step
pulses. The subsequent clear operation of this step counter may be
executed either by a signal dedicated to command a count-clear
operation transmitted from the CPU as shown or by effectively
utilizing the ON/OFF signal from the CPU.
The platen roller 31 is disposed coaxially on a drive shaft of the
stepping motor M to be driven by this motor M. the diameter of this
platen roller 31 is set to be a multiple of an integer of
one-step-unit film transport distance covered by a predetermined
one frame pitch of the film 11 provided by one step amount drive of
the stepping motor M. In this embodiment, this diameter R is set to
be 31.831 mm obtained from the expression shown below and the frame
pitch of the film 11 is set to be 10 mm. Thus, for transporting the
film 11 by one frame pitch, the stepping motor M effects a drive
corresponding to forty steps units.
where N is the number of steps of the stepping motor for
transporting the film by one frame pitch, P is a length of the one
frame pitch of the film, and A is the step angle of the stepping
motor.
The platen roller 31 is disposed in a position opposed to a
direction in which a portion of its outer circumferential face is
irradiated by the laser beam applied from the image information
recording section 40 to be described later, the above opposing
position being an image-recording position. At the left and right
sides of this image-recording position, there are disposed the
pressing rollers 32 and 33 contacting the outer circumferential
face of the platen roller 31. The film 11 having been delivered
from the film delivery section 10 is transported as being pressed
against an outer circumferential face of the platen roller 31 by
the pressing rollers 32 and 33 while the film contacting the
image-recording position.
The image information recording section 40 comprising a laser
optical unit records image information by applying the laser beam
to the film being transported at the image-recording position of
the platen roller 31 in a width direction of the film 11 (direction
being normal to the film transport direction). More particularly,
this image information recording section 40 includes a laser device
41 for generating a helium neon gas laser based on predetermined
image information, a rotary polygon mirror 42 effecting a line
scanning operation by causing a high-speed eccentric rotation of
the laser beam from the laser device 41, and a lens group 43 for
forming an image at a distance proportional to an incident angle of
the laser beam from the rotary polygon mirror 42.
The heat-developing section 50 heat-develops the image information
recorded on the film 11 by the image information recording section
40, and is disposed inside the housing between the film transport
unit 30 and the film accommodating section 20 while facing the film
transport passage 26. This heat-developing section 50 includes a
heating roller 51 having an outer circumferential face 51a for
heating the film 11 contacting the face and a guide roller 52 for
advancing the heat-developed film 11 to the film accommodating
section 20.
Also, at the film feed side of the platen roller 31, there are
provided a film slack detecting device 7 for detecting slacks of
the film 11 being transported and feed drive rollers 34 and 35
driven as being controlled based on a detection by the film slack
detecting device 7. At the film discharge side of the platen roller
31, on the other hand, there are provided, in a similar fashion as
the above-described film feed side, another film slack detecting
device 8 and film discharge drive rollers 36 and 37. The film slack
detecting devices 7 and 8 comprise infrared light emitting diodes
7a and 8a and light receiving elements 7b and 8b, respectively.
On the film transport passage 26 between the heat-developing
section 50 and the film accommodating section 20, there are
provided a transport drive roller 52 and an image density detector
56 for detecting a density of the image information heat-developed
on the film 11 and for adjusting an irradiation amount of the laser
beam from the laser device 41 based on the detection. This image
density detector 56 comprises a light emitting diode 56a and a
light receiving element 56b disposed respectively on the sides
across the film transport passage 26.
Next, functions of the image forming apparatus of the present
invention constructed as above, will be particularly described.
The roll film 11 of the heat-developing type is pre-loaded in the
film delivery section 10, with its leading end being extended into
the film transport passage 26 to be taken up by the take-up reel 21
of the film accommodating section 20. Alternatively to this
arrangement, the leading end of the film 11 may also be discharged
onto the film tray 22 disposed externally of the housing by means
of an appropriate switching device.
From this condition, as the image forming apparatus is powered ON,
the film delivery section 10, the platen rollers 34 and 35 and the
discharge drive rollers 36 and 37 are activated, whereby the film
11 having been delivered from the film delivery section 10 is
advanced with a suitable slack provided by the feed drive rollers
34 and 35 to the platen roller 31. In the above operations, the
slack detecting device 7 detects the amount of slack of the film 11
being transported, and based on a resultant detection signal from
this device 7 the drive speed of the feed drive rollers 34 and 35
is adjusted. Then, the film 11 is transported while being urged by
the pressing rollers 32 and 33 against the image-recording position
on the outer circumferential face of the platen roller 31 being
driven by the stepping motor. In synchronism with the above
operations, the film 11 has its face opposed to the other face
contacting the platen roller 31 irradiated by the laser beam from
the image information recording section 40, on which face image
information is recorded. In this image information recording
operation, the stepping motor M drives microstep-wise the platen
roller 31 through the microstep driver MSD. When the platen roller
31 has transported the film 11 by one-frame unit length (10 mm),
the stepping motor M has rotated by exactly 40 steps units. As the
result, when the film 11 has been transported by a predetermined
amount, either pair of the rotors of the stepping motor is always
stopped at a position opposed to as being attracted by the stator.
Accordingly, the rotor pair is not moved inadvertently after
completion of predetermined amount of transportation of the film
11, and the leading edge of the next frame to be formed with a
subsequent drive of the stepping motor is always placed at the
predetermined leading edge position of the frame pitch. Thereafter,
the film 11 having its face recorded with the image information is
discharged through the platen roller 31 while being provided with
an appropriate slack by the discharge drive rollers 36 and 37
controllably driven by the slack detecting device 8, then the film
11 is fed to the heat-developing section 50, where the film 11 is
heat-developing as its face opposite to the face recorded with the
image information through the foregoing laser beam irradiation
being heated by the heating roller 51 of the heat developing
section 50. This heat-developed film 11 then undergoes an image
density detection by the image density detector 50 and is
transported by the transport roller into the film accommodating
section 20.
As described above, according to the image forming apparatus of
this embodiment of the present invention, it is possible not only
to transport the film 11 with a high precision but also to maintain
the frame pitch exactly constant.
Further, if a step counter is provided to the control section for
the stepping motor, it is possible to achieve the above effect
without significantly modifying the prior art apparatus.
Also, as described hereinbefore, the main drive roller 31
transports, for feeding or discharging, the film 11 being provided
with an appropriate slack. Therefore, the roller 31 is not
subjected to any tensile force from the film 11 and thus achieves a
stable rotational speed for driving.
(Modified Embodiment)
In this modified embodiment, the control section for controlling
the stepping motor includes a drive counter in place of the step
counter used in the previous embodiment. In this case, referring to
FIG. 4 showing its control block, the drive counter is set to drive
the microstep driver by 40 steps (N) in response to an input of an
ON signal from the CPU.
The image forming apparatus of this modified embodiment is
advantageous in that the CPU is less burdened with operations than
that of the apparatus of the previous embodiment while achieving
the same effect as the latter.
More particularly, in the case of the image forming apparatus by
this modified embodiment, the platen roller has such a diameter
that the predetermined one frame unit film transport distance is a
multiple of an integer of the stepwise transport distance covered
by one step amount rotation of the stepping motor. As the result,
when a predetermined amount of film transport is completed, the
stepping motor is always stopped at a magnetically stable position
where either pair of the motor rotors is opposed and attracted to
the stator. Accordingly, the frame pitch may be maintained very
constant, and the leading edge of the next image may be always
placed at the predetermined leading edge position of the frame
pitch. Thus, with such the simple driving device, both the film
transport and frame edge positioning operations may be carried out
effectively.
(Embodiment (2 ))
An image forming apparatus according to this second embodiment of
the present invention uses a control section including a CPU, a
microstep driver and a step memory driver as shown in a control
block in FIG. 5. The CPU controls the entire image forming
apparatus and operates to energize or de-energize the microstep
driver and the step memory driver by transmitting pulse signals
thereto in synchronism with a laser irradiation for image
information recording. The microstep driver, in response to an
ON/OFF signal from the CPU, drives the stepping motor 1
microstep-wise by sub-dividing one step unit of the motor into 1024
microsteps, this microstep driver includes a memory to be described
later. The step memory driver, in response to an ON signal from the
CPU, causes the microstep driver to effect a drive operation by the
number of microsteps stored in the memory. This drive operation by
the step memory driver, it is to be noted, is effected after the
stepping motor is driven by one step reverse in case the motor was
stopped at a step position advanced from that assumed by the motor
at the completion of the previous microstep driving operation.
The memory disposed in the microstep driver operates to store the
number of microsteps of the microstep driver having driven the
stepping motor. More specifically, providing the stepping motor is
stopped at a certain step position, this step position as well as
the other step positions is sub-divided into 1024 microsteps units
by the microsteps driver as described above. Then, the memory
stores the number of microstep units within the above step counted
from the microstep position first in the order to the microstep
position assumed by the motor at the completion of the previous
microstep driving operation. This memory preferrably comprises the
nonvolatile type or the battery-backed-up type so as to retain its
memory contents when the power supply to the entire apparatus is
stopped.
When image information is recorded on the film by laser beam
irradiation, the stepping motor is driven microstep-wide by
receiving via the microstep driver the pulse signals from the CPU,
thereby driving the platen roller 31 smoothly. When this image
information recording operation is completed, the CPU stops
transmitting the pulse signals to the stepping motor via the
microstep driver, whereby the stepping motor is de-energized to
stop transporting the film 11 through the platen drive roller 31.
In the above operations, if the stepping motor stops receiving the
pulse signals from the CPU at n microstep position
(0.ltoreq.n.ltoreq.1023) in the middle of its one step rotation
unit sub-divided into 1024 microsteps, the stepping motor comes to
a halt only after returning (n<512) or advancing (n.ltoreq.512)
to stable step position. That is to say, as described in the
beginning of this specification the stepping motor, because of its
inherent characteristics, is in a magnetically balanced or stable
state when either of its rotor pairs is opposed to by the stator as
the rotor pair and the stator being magnetically attracted to each
other. In other words, such stable position corresponds to each
step position of the motor. Thus, if the drive pulse signal
transmission to the motor is stopped in the middle of one step, the
motor will stop rotating at the angularly closer stable position
displaced either clockwise or counterclockwise from the position
previously assumed by the motor before the cessation of the signal
input. Therefore, when each step is sub-divided into 1024
microsteps as in this embodiment, providing the number of
microsteps at the moment of signal input interruption being n, if n
is smaller than 512, the stepping motor return by n microsteps. On
the other hand, if n is larger than 512, the stepping motor
advances by 1024-n to the beginning of the next step position.
This number n of microsteps is stored in the memory. Thereafter,
when receiving the next ON signal from the CPU, the stepping motor
is driven through the microstep driver in accordance with a flow
chart shown in FIG. 6. It is to be noted that this flow chart
illustrates only the routine immediately related to the present
invention, i.e., the routine for setting the frame edge leading
position by the stepping motor. With start of this routine, the
program reads through the step memory driver the microstep number n
stored at the memory of the step memory driver. Then, the program
judges whether the value n is smaller than 512. When YES, the step
memory driver causes the microstep driver to effect a driving
operation dictated by the microsteps of the value n. From this
condition, the stepping motor starts a microstep driving operation
in synchronism with a laser beam irradiation by the image
information recording section 40. Thus, the leading edge of the
image to be formed nextly on the film 11 with a subsequent drive of
the stepping motor is always set at the predetermined leading edge
position of the frame pitch. Then, the film 11 having recorded this
image information is discharged and transported with an appropriate
slack by the discharge drive rollers 36 and 37, which are driven
and controlled by the slack detecting device 8, to proceed to the
heat-developing section 50.
(Modified Embodiment 1)
In this modified embodiment related to the second embodiment of the
present invention, the number of microsteps is stored in a memory
of the CPU in place of the memory of the microstep driver.
Referring to a a control block diagram in FIG. 7, in response to an
ON/OFF signal from the CPU, the microstep driver drives the
stepping motor microstep-wise. This number of microsteps is stored
in a step memory of the CPU. Thereafter, when the CPU again
transmits an ON signal to the microstep driver, the microstep
driver starts driving the stepping motor after setting the motor to
a position corresponding to the position where the previous
microstep driving operation was terminated.
The above-described image forming apparatus of this modified
embodiment is capable of achieving the same effect as of the
previously described second embodiment without providing the
dedicated memory driver or the like.
(Modified Embodiment 2)
In this further modified embodiment related also to the second
embodiment, the microstep driver is controlled by a step controller
having a memory. In this case, as illustrated in a control block
diagram in FIG. 8, the microstep driver receives an ON/OFF signal
from the CPU through the step controller and then drives the
stepping motor microstep-wise. This number of microsteps is stored
in the memory of the step controller. Thereafter, when the CPU
again transmits an ON signal to the step controller, the step
controller carries out a control operation such that the stepping
motor is re-energized after the motor is set to a position
corresponding to the position where the previous microstep driving
operation was stopped.
In the above-described image forming apparatuses according to the
second embodiment and its first and second modified embodiments of
the present invention, the main drive unit includes the stepping
motor driven in terms of a plurality of microsteps constituting a
sub-divided step of the motor, the platen roller driven by the
stepping motor for transporting the film contacting the outer
circumferential face of the roller, the memory for storing the
number of microsteps provided by the stepping motor and
representative of the film transport distance provided by the main
driver roller, and the control section for effecting a control
operation based on the stored contents in the memory such that the
next driving operation of the stepping motor is started after the
motor is set to the position where the previous microstep driving
operation was stopped.
Consequently, even if an image forming operation on the film is
stopped in the middle of one step unit of the stepping motor, the
next image forming operation is started with the leading edge of
the image to be formed next being returned to the position
previously assumed by the motor at the completion of foregoing
driving operation. Therefore, the leading edge of the image to be
formed next is always set to the predetermined leading edge
position of the next frame pitch. As a result, the adjacent images
to be formed in series on the film will not overlap with each other
in the transport direction of the film. As described above,
according to the present invention, the film transport operation
and the positioning operation of the leading edge of the image to
be formed on the film may be effectively carried out by a single
drive unit having such simple construction as described above.
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